1. Field of the Invention
The present invention relates to a surface acoustic wave device used for resonators and bandpass filters and more particularly, to an edge reflection type surface acoustic wave device having a construction in which a Shear Horizontal (SH) type surface acoustic wave is reflected between two opposing end surfaces and a manufacturing method for the same.
2. Description of the Related Art
Various edge reflection type surface acoustic wave devices using of SH waves such as a BGS wave, a lobe wave, etc., reflected between confronting end surfaces have been proposed.
In the edge reflection type surface acoustic wave device, the SH wave is reflected between the opposing two end surfaces, and, in this case, there is a problem that, when unnecessary waves other than the SH waves are reflected at the end surfaces, undesired ripples appear in the characteristics and the deviation of GDT (group delay time characteristics) increases.
In Japanese Unexamined Patent Application Publication No. 4-82315, a construction in which a bulk wave producing unnecessary spurious noise is suppressed, is shown in an edge reflection type surface acoustic wave device. Here, stair portions are provided at a height which is a thickness portion of the piezoelectric substrate where 80% of the energy of the SH wave is concentrated or farther away from the surface of the piezoelectric substrate, on the opposing two end surfaces which are used as reflection end surfaces. The energy of a bulk wave spreads over the entire thickness area of the piezoelectric substrate, but, on the other hand, the energy of the SH wave is concentrated in a layer that is close to the surface of the piezoelectric substrate. Therefore, in this prior art device, the above-noted difference of deviation of the energy between the SH wave and a bulk wave is utilized and the resonance of the SH wave is effectively utilized in the layer of the piezoelectric substrate on the surface side of the piezoelectric substrate beyond the stair portion. On the other hand, the resonance of a bulk wave has no effect in the layer of the piezoelectric substrate that is lower than the stair, and accordingly, the spurious noise to be produced by a bulk wave is suppressed.
Furthermore, in this prior art, it is also shown that irregular reflection of a bulk wave is produced by making the end surface portions which are lower than the stair, a rough surface and, as a result, the resonance energy of a bulk wave is reduced.
However, in this prior art, it is also shown that it is not necessary to make the end surface portions which are lower than the stair a rough surface.
Furthermore, in FIG. 5 of the 4-82315, a construction in which second and third end surface portions are formed two stairs away from end surface portions provided on the side of the surface on which the electrodes of the piezoelectric substrate are formed and below the end surface portions, is shown, and here, it is also shown that, below each stair, the second and third end surface portions may be appropriately made to have a rough surface.
As disclosed in Japanese Unexamined Patent Application Publication No. 4-82315, in the past, a method in which, in an edge reflection type surface acoustic wave device, the end surfaces are made to have a rough surface in order to suppress the reflection of unnecessary waves such as a bulk wave, etc., on the end surfaces is shown. However, when two opposing end surfaces of a piezoelectric substrate are cut by using a blade under the condition that the end surfaces become a rough surface, there is a problem in that cracks are produced on the end surfaces and in that chipping is likely to occur in the edge portion between the end surface and the bottom surface of the piezoelectric substrate.
That is, it is very difficult to obtain an edge reflection type surface acoustic wave device in which ripples and spurious noise are fully suppressed and cracks, chipping, etc., are not produced.
In order to overcome the problems described above, preferred embodiments of the present invention provide a method of manufacturing an edge reflection type surface acoustic wave device in which the above-described defects in the prior art are solved, the degradation of characteristics due to the reflection of unnecessary waves on the end surfaces is prevented from occurring, and cracks and chipping are prevented from occurring, and also provide an edge reflection type surface acoustic wave device produced by such a method of manufacturing.
A preferred embodiment of the present invention provides a method of manufacturing an edge reflection type surface acoustic wave device including a piezoelectric substrate having opposing two end surfaces and at least one IDT provided on the piezoelectric substrate and in which an SH type surface acoustic wave is reflected between the opposing two end surfaces, the method including the steps of preparing a piezoelectric substrate, forming at least one IDT on the upper surface of the piezoelectric substrate, performing a first half cut in the piezoelectric substrate in order to form opposing two end surfaces defining reflection end surfaces in which the piezoelectric substrate is half cut from the upper surface of the piezoelectric substrate to a depth not reaching the lower surface of the piezoelectric substrate by using a first blade such that first end surface portions having a smooth surface defining reflection end surfaces are formed, performing a second half cut in which, after the first half cut, the piezoelectric substrate is cut to a depth not reaching the lower surface of the piezoelectric substrate by using a second blade so as to form second end surface portions having a rough surface such that the second end surface portions of the rough surface are arranged below the first end surface portions on the outside of the first end surface portions in the surface acoustic wave propagation direction, and performing a full cut in which the piezoelectric substrate is cut by using a third blade so as to reach the lower surface of the piezoelectric substrate at a location outside of the second end surface portion in the surface acoustic wave propagation direction.
In this preferred embodiment of the present invention, the first half cut, the second half cut, and the full cut are performed when the substrate is in the state of a mother piezoelectric wafer. The mother piezoelectric wafer is divided to obtain separate individual surface acoustic wave devices in the step of performing the full cut. Accordingly, an edge reflection type surface acoustic wave device can be effectively mass-produced from a piezoelectric wafer in accordance with preferred embodiments of the present invention.
In this preferred embodiment of the present invention, the second half cut may be performed before or after the step of performing the full cut.
In this preferred embodiment of the present invention, the thickness of a second blade used in the step of performing the second half cut is larger than the thickness of a third blade used in the step of performing the full cut. Accordingly, the second half cut is formed in a mother piezoelectric wafer by using the second blade to form a groove. Then, a full cut is performed in the groove using the third blade, the thickness of which is smaller than the second blade and, as a result, the adjacent edge reflection type surface acoustic wave devices can be surely cut below the second end surface portions.
In a preferred embodiment of the present invention, the second half cut is performed twice by displacing the second blade in the surface acoustic wave propagation direction, and the full cut is performed by using the third blade, the width of which is smaller than the width in the middle of the groove. In this case, since a groove, the width of which is larger than the thickness of the second blade in the step of the second half cut, a full cut can be easily performed using a third blade which is thinner than the width of the groove.
In this preferred embodiment of the present invention, the full cut is performed after the step of performing the first half cut and then the step of performing the second half cut is executed. Thus, in a method of manufacturing according to the first preferred embodiment of the present invention, the full cut is not necessarily required to be performed after the step of performing the second half cut. Even if the full cut is performed before the step of performing the second half cut, the second half cut can be executed so as to surely make the second end surface portion a rough surface in the step of performing the second half cut. Moreover, in this case, in the step of performing the second half cut, the second end surface portion linked below the first end surface portion is formed above the last end surface portion formed in the full cut.
In a preferred embodiment of the present invention, the method of manufacturing an edge reflection type surface acoustic wave device further includes a step of performing a second full cut, in which a mother piezoelectric wafer is full cut in the direction that is substantially perpendicular to the reflection end surface in order to obtain separate individual surface acoustic wave devices from the mother piezoelectric wafer, and the second full cut is performed before the steps of making the first half cut, the second half cut, and the full cut. In this case, the second full cut is performed such that each of surface acoustic wave devices are linked on the side of the opposing two end surfaces, and then the first half cut, the second half cut, and the full cut are performed in accordance with preferred embodiments of the present invention. Therefore, it is desirable to execute the first half cut, the second half cut, and the full cut in the strip-shaped piezoelectric wafer portion. This is because the effect of the pressure to be applied to a piezoelectric wafer can be reduced when the wafer is mounted to or removed from a dicer.
Furthermore, the second full cut may be performed between the step of the first cut and the step of the second half cut. Also in this case, it is desirable to execute the first cut, the second cut, and the full cut in the strip-shaped piezoelectric wafer portion. This is because the effect of the pressure to be applied to a piezoelectric wafer can be reduced when the wafer is mounted on or removed from a dicer.
In a preferred embodiment invention, an edge reflection type surface acoustic wave device, in which a first end surface portion and last end surface portion having a smooth surface and a second end surface portion having a rough surface are provided, can be obtained in accordance with the present invention.
Another preferred embodiment of the present invention provides an edge reflection type surface acoustic wave device including a piezoelectric substrate having two opposing end surfaces defining reflection end surfaces, at least one IDT disposed on the piezoelectric substrate, first end surface portions having a smooth surface and defining two opposing end surfaces extending from the upper surface to a height not reaching the lower surface of the piezoelectric substrate, last end surface portions having a smooth surface extending upward from the lower surface of the piezoelectric substrate and disposed outside of the first end surface portions in the surface acoustic wave propagation direction, and second end surface portions having a surface roughness Ra of approximately 0.006xcex or greater, disposed between the first end surface portions and the last end surface portions.
In an edge reflection type surface acoustic wave device according to this preferred embodiment of the present invention, since the smooth first end surface portions and last end surface portions and the second end surface portions having a rough surface with a surface roughness Ra of about 0.006xcex or more, which is disposed between the first end surface portions and last end surface portions, are provided as two opposing end surfaces, undesirable reflections of unnecessary waves are effectively prevented at the second end surface portions. Accordingly, the first end surface portions function as reflection end surfaces and the SH wave is reflected very well and the degradation of characteristics due to the reflection of unnecessary waves on the opposing two end surfaces is reliably prevented.
In an edge reflection type surface acoustic wave device of a preferred embodiment of the present invention, when the dimension in the depth direction of the first end surface portions is represented by d1, it is preferred that 1.8 xcexxe2x89xa6d1xe2x89xa63.5 xcex, and, in this case, as clearly understood in the preferred embodiment described later, the reflection of unnecessary waves is even more effectively prevented.
Furthermore, in an edge reflection type surface acoustic wave device of a preferred embodiment of the present invention, when the dimension in the depth direction of the first end surface portions is represented by d2, it is preferred that d2xe2x89xa70.5 xcex, and, in this case, degradation of characteristics due to the reflection of unnecessary waves at the opposing two end surfaces is even more effectively prevented.
An edge reflection type surface acoustic wave device of another preferred embodiment of the present invention includes a piezoelectric substrate having two opposing end surfaces defining reflection end surfaces, at least one IDT disposed on the piezoelectric substrate, first end surface portions having a smooth surface defining the reflection end surfaces and extending from the upper surface to a height not reaching the lower surface of the piezoelectric substrate, last end surface portions having a smooth surface extending upward from the lower surface of the piezoelectric substrate and disposed outside of the first end surface portions in the surface acoustic wave propagation direction, and second end surface portions having a rough surface and disposed between the first end surface portions and the last end surface portions, wherein when the dimension in the depth direction of the first end surface portions is represented by d1, 1.8 xcexxe2x89xa6d1xe2x89xa63.5 xcex.
An edge reflection type surface acoustic wave device of another preferred embodiment of the present invention includes a piezoelectric substrate having two opposing end surfaces defining reflection end surfaces, at least one IDT disposed on the piezoelectric substrate, first end surface portions having a smooth surface defining the reflection end surfaces extending from the upper surface to a height not reaching the lower surface of the piezoelectric substrate, last end surface portions of a smooth surface extending upward from the lower surface of the piezoelectric substrate and disposed outside of the first end surface portions in the surface acoustic wave propagation direction, and second end surface portions of a rough surface and disposed between the first end surface portions and the last end surface portions, wherein when the dimension in the depth direction of the second end surface portions is represented by d2, d2xe2x89xa70.5 xcex.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.